Continuous mixer

ABSTRACT

A mixer for use particularly in the dispersion of powders in gelatinous masses and for the handling of the resultant mixtures, applicable especially to the rubber and plastics industries in general, in which a single mixing chamber is used together with a single rotor consisting of a number of sections inside said chamber.

United States Patent Aletti CONTINUOUS MIXER [72] Inventor: RenatoAIettI, Via Sempione 14, 21100 7 Varese, Italy [22] Filed: May 15, 196921 Appl. No.: 824,995

[30] Foreign Application Priority Data May 18, 1968 Italy ..16671 A/68[52] U.S. CI. ..259/7, 18/2 ES, 18/12 SA,

18/12 SB, 18/12 SE, 18/12 SN, 259/9, 259/43, 259/97 [51] Int. Cl. ..B01f7/24, B01f7/08 [58] Field of Search ....259/2, 17, 35, 59, 93, DIG. 3,259/DIG. 4, DIG. 6, DIG, 10, DIG. ll, DIG. 13, 9, 10, 45, 46,109,110

[56] References (Iited UNITED STATES PATENTS 1,935,050 11/1933 Gordon3,154,808 11/1964 Ahlefeld, Jr. eta

1451 May 9,1972

1,424,445 8/1922 Bowen & Schnuck ..259/DIG. 13 2,581,031 1/1952 Kruzik3,023,455 3/1962 Geier et al. ..259/2 3,164,375 1/1965 FrenkeL. ..259/93,189,324 6/1965 Gubler... 259 109 3,347,528 10/1967 List et a1. ..259/23,416,774 l2/l968 Frltsch ..259/ 109 FOREIGN PATENTS 0R APPLICATIONS749,833 1/1967 Canada 4259/9 Primary Examiner-William 1. Price AssistantE.\'amir1er-Alan I. Cantor Anorney-Stevens, Davis, Miller & Mosher 57ABSTRACT A mixer for use particularly in the dispersion of powders ingelatinous masses and for the handling of the resultant mixtures,applicable especially to the rubber and plastics industries in general,in which a single mixing chamber is used together with a single rotorconsisting of a number of sections inside said chamber.

10 Claims, 5 Drawing Figures PATENTEDMM 9 I972 3,661,363

SHEET 1 UF 3 REA/H To Inventor fiat/1r, L now ww ww A llorneyyPATENTEDMAY 9 I972 SHEET 3 OF 3 INVENTOR RENATO ALETTI BY m 06 MJIMATTORNEYS BACKGROUND OF THE INVENTION This invention relates to acontinuous extended surface mixer which is particularly suitable forapplication to the rubber, plastic, soap, edible flour product and otherindustries, for use in the dispersion of powders in gelatinous massesand for the handling of the resultant mixtures.

Many types of mixtures are known in this field which are capable ofbeing used with good results for the above mentioned applications.Essentially these are required to perform a double function, this beingto carry out macroscopic mixing of the ingredients fed to it and toobtain a fine dispersion of a certain type of these ingredients,generally a powder, in others which may be extremely viscous pastes orrelatively viscous liquids. Because of the particular development oftheir field of application the mixers in question are objects ofcontinuous and deep study with the purpose of ever improving their useand efficiency both from the point of view of process quality andproductive output.

This invention adds a valid contribution to these studies by providing amixer with improved characteristics from both the aspects mentioned, inthat it is able on the one hand to give continuous production and on theother hand to provide improved processing of the mixtures.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is asectional view of the essential parts of the mixer according to theinvention through the axis of its rotor;

F IG. 2 is a transverse section through the line Il-II of FIG. 1;

FIG. 3 shows one embodiment of the detail enclosed 'by the circle C ofFIG. 2;

FIG. 4 shows an alternative embodiment of said detail; and

possible. In the drawing this type of assembly, which can be carried outin practice in a number of different ways, is shown diagrammatically asa fixing by means of bolts b through a continuous slot f of theframework M. The chamber rests on a plurality of screws v (only one ofwhich is illustrated in FIG. I) carried by internal threads m of theframework M so that the axial position of the chamber 2 can be exactlyadjusted and its 1 axis maintained vertical. By rotating these screwstogether the FIG. 5 is a sectional view, similar to FIG. 1, showing anal- I ternative embodiment of the rotor.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawings themixer illustrated comprises a feed hopper l, a cylindrical or slightlyconical chamber 2 with vertical axis surrounded by an external shell 3which forms an interspace 4 for the circulation of a means of heatexchange and a rotor 5 arranged so that a large part of its length isinside the chamber 2 and having its axis coincident with that of saidchamber. The rotor 5 consists of a single elongated body of steelcomprising cylindrical extremities 6, at least one of which issupported, and a central working part. The working part comprises a feedscrew conveyor 7 which functions as an I element for feeding and dosingthe material, a mixing section 8 formed from two opposing screw parts 80and 8b and a third prismatic part 8c, and finally a discharge section 9in the form of an inverted truncated cone. The chamber 2 terminates atits lower end with a discharge ring 10 shaped conically internally withan angle different from that of the discharge section 9 of the rotor 5which is arranged inside it. The interspace 4 is divided into twosections 4' and 4" fed by way of holes 4" with the purpose of permittingbetter temperature control inside the mixing chamber.

The chamber 2 is fixed to the framework M of the machine in such a waythat small variations in its axial position are level of the chamber 2is varied and as the position of the rotor 5 remains fixed, as will beseen hereinafter, a relative axial movement between these parts of themixer takes place. This permits the width of the annular cavity whichseparates the discharge ring 10 of the chamber 2 from the dischargesection 9 of the rotor 5 to be .modified whenever this is necessary foradaptation to the individual process runs.

The screw system v described can obviously be substituted, in a type ofmixer according to the invention having more advanced characteristicsthan that diagrammatically described, by a hydraulic system of morecomfortable and reliable operation. This system could thus be employednot only now and again, between one operation of the machine and anotheror between one stage of the operation and another, but even during theprogress of each individual operation, in order to vary the dischargesection and thus permit the regulation of one of the process variables.An analogous result could also be obtained by means of motorization ofthe screw system described and illustrated.

It is important to note the fact that the mobility of level of thechamber 2 renders the cleaning of the machine easy. In

fact by removing the hopper l and the discharge ring 10, the

whole body of the mixer can be raised so uncovering the mixing and feedscrew conveyor sections for cleaning. The chamber 2 can then be easilycleaned as can the other parts of the mixer.

Lateral holes 2' are provided in the chamber 2 at different heights withthe purpose of permitting the introduction into the mixing chamber ofelements for'measuring the process variables, in particular temperatureand pressure. Said holes 2 or similar holes ofsuitable size can be usedfor the introduction of additional materials of any type into the mixingchamber 2.

In FIG. 1 the rotor 5 is shown rotablysupported at its lower end in asupport comprising radial bearings 11 and thrust bearings 12. At itsupper end the rotor can be supported by a radial bearing (not shown) orcan terminate (as indicated by the broken lines 5') without furthersupport.

The rotor is driven at one of its ends by any suitable known systemeither at fixed or variable velocity according to requirements. It isnot considered necessary to illustrate any of these systems in detail inthe figures, neither does it serve any purpose to describe one here.

Examining in greater detail the characteristics of the rotor 5 it isseen that the feed screw conveyor 7 is shown formed with a squaresection. This section could however be slightly trapezoid withoutnegative consequences. It is however important that the feed capacity ofthe screw is in line with the general characteristics of the mixer.

The section of the screw zones 80, 8b and 80, clearly shown in- FIG. 2,are in the form of an equilateral triangle, with the corners 13bevelled. By making the bevels 13 with a circumference concentric withthe external chamber 2, the width of the gap h will be constant, as inthe case of FIG. 3. The direction of rotation indicated by the arrow Fis fixed only by the necessity for the screw 7 to push the material intothe chamber, in that the section itself does not have an inherentdirection of rotation. The upper screw zone has to push the materialdownwards while the lower zone 8b has to force it upwards so as to remixthe material. Alternatively the gap h can be made of variable width bymaking bevels 13 formed from a flat wall sp and a curved part so withits center of curvature displaced from the axis of the rotor, as shownin FIG. 4. In this case the direction of rotation has to be thatindicated by the arrow F. It is also possible to form the parts 8a and 8b of the rotor with triangular sections having cylindrical bevels 13concentric with the axis and the part 8c of triangular section havingflat and curved bevels 13'.

The bevels l3 and 13 consist of surfaces parallel to the axis of themachine when the chamber 2 is cylindrical. When the chamber 2 isslightly conical the bevels can also be shaped with conical or inclinedsurfaces which among other things will allow the width of the gap h tovary as a function of the reciprocal axial position of the chamber 2 andthe rotor 5.

The rotor 5 is preferably made with an axial bore to allow thecirculation of a heat exchange fluid. The method of effecting this istechnically well known and there is no need to illustrate it. For thisreason and for simplicity it has not been shown on the drawings.

The operation of the mixer can be described briefly: The materials to bemixed are loaded into the hopper 1 in suitable forms and quantities. Thescrew conveyor of the rotor 7 feeds them into the chamber 2 and thruststhem downwards into the mixing zone formed by the two triangular screwparts 8a and 8b of the rotor, the first part of which forces thematerial downwards and the second upwards, so as to create idealconditions for an efficient and intimate mixing. The material thenpasses into the zone corresponding to the part 80 by the thrust of thefresh material, created by the screw conveyor 7, then through thedischarge zone between the discharge section 9 and the rotor 5 and thedischarge ring l0, to the outside of the machine. Along the whole of thelength of the chamber 2 the material being handled is subjected totemperature and pressures which are adjusted by varying the temperatureof the heat exchange fluids circulating in the interspaces 4' and 4" andinside the rotor 5 respectively, and by varying the relative levelbetween the chamber 2 and the rotor 5 and the rotational speed of therotor. The extent and influence of the individual adjustments will varyaccording to the material and processes being operated, according torules easily determinable by specialists.

At the beginning of operation there will be a transitory period duringwhich the mixing chamber is filled. After this the operation willproceed continuously according to substantially constant laws.

The mixer according to the invention gives considerable advantages overconventional ones. Its particular characteristics are its extremestructural simplicity, the vertical flow of the material and the highintensity os mixing and dispersion which can be obtained by it.

With regard to the simplicity of structure of the mixer it will be seenfor example that axial discharge of the product allows the complicatedsystems usually necessary for rendering the mixing chamber tight to beeliminated. Another important characteristic is the extended surface perunit of volume of material being processed, this permitting a highdegree of heat exchange between the walls of the mixing chamber centralrotor and material, so facilitating temperature control of material. Theoperation of the machine is continuous and this constitutes anunquestionable and substantial factor of progress to which must be addedthe ease, simplicity and reliability of operation and adjustment, easeof cleaning and compactness of the structure.

The described embodiment of the mixer according to the invention, beingby way of example only, can undergo variations and modifications ofvarious kinds without leaving the field of protection of the invention.To give some examples the rotor 5 can be supported at its upper partrather than its lower part by using an upper support furnished withthrust bearings. The shape of the section of the parts 8 of the rotorcan also be varied by making the sides of the triangle which form itcurved for example. Similarly the crests of the screws of the rotor,which are discontinuous in the representation shown in the drawings, canbe made continuous wholly or partly. The interspace sections can be morethan two or the interspaces can be substituted by spirals 24 which canbe filled either with heat exchange fluid or electrical heating coilmeans. It has already been said that the assembly of the mixin chamberon the framework of the mixer can be made in a ifferent manner. It

can be added that the chamber itself and its shell can be made in twohalves in order to facilitate cleaning and removal of the chamber.

Finally it should be noted that although the mixer according to theinvention derives important advantages from the venical arrangement ofits parts it can also be built horizontally, so conserving all thoseadvantages which do not depend on the principal position of the machine.

Although the machine is here claimed and described as a complete machinein itself it will be evident to specialists in the field that it canalso form the central part of an extruder or an injection press. Theinvention also applies to this particular application.

I claim:

1. A mixer for use particularly in the dispersion of powders ingelatinous masses and for the handling of the resultant mixtures,applicable especially to the rubber and plastics industries in general,comprising a substantially cylindrical mixing chamber having a smoothinner surface and a single rotor coaxial with said chamber and rotatingtherein, said rotor having three continuous sections for feeding, mixingand discharge, respectively, of which the mixing section is formed fromtwo opposing screw parts and a prismatic part, said screw parts beinggenerated by the rotation, in opposite directions along the rotor axis,of a plane polygonal section equal to that of said prismatic part.

2. A mixer as claimed in claim 1, in which the feed section of the rotorcomprises a screw conveyor and the discharge section comprises aninverted truncated cone, further comprising a feed hopper secured to thefeed end of said chamber, said rotor being arranged inside the mixingchamber in such a way that the feed section projects outwards from thechamber to penetrate into said feed hopper, and a discharge ring on thedischarge end of said chamber having its internal wall in the shape of atruncated cone with a taper different from that of the discharge sectionof the rotor.

3. A mixer as claimed in claim 2, further comprising means to adjust thedischarge area fonned between the discharge ring of the mixing chamberand the discharge section of the rotor by relative axial movement of theparts forming said area.

4. A mixer as claimed in claim 3, in which the mixing chamber furthercomprises interspaces for circulation therein of a heat exchange fluid,means to circulate said fluid inside the rotor and inside the dischargesection of the chamber.

5. A mixer as claimed in claim 1, further comprising means forrelatively moving the rotor and mixing chamber along a common axis andin which the material feed and discharge are simultaneous andcontinuous.

6. A mixer as claimed in claim 1, further comprising closable holes insaid chamber which permit the introduction into the chamber of membersfor sensing the parameters of the operational process and/or of processmaterial.

7. A mixer as claimed in claim 1, in which the mixing chamber and therotor are cylindrical.

8. A mixeras claimed in claim 1, in which the mixing chamber and therotor are slightly conical.

9. A mixer as claimed in claim 1, in which the feed section of the rotorcomprises a screw conveyor while the discharge section comprises aninverted truncated cone and the mixing section has a triangle as thecross-section of its screw and prismatic parts.

10. A mixer as claimed in claim 9, in which the corners of the triangleof said section are bevelled according to a circumference concentricwith the axis of the mixing chamber and rotor.

1. A mixer for use particularly in the dispersion of powders ingelatinous masses and for the handling of the resultant mixtures,applicable especially to the rubber and plastics industries in general,comprising a substantially cylindrical mixing chamber having a smoothinner surface and a single rotor coaxial with said chamber and rotatingtherein, said rotor having three continuous sections for feeding, mixingand discharge, respectively, of which the mixing section is formed fromtwo opposing screw parts and a prismatic part, said screw parts beinggenerated by the rotation, in opposite directions along the rotor axis,of a plane polygonal section equal to that of said prismatic part.
 2. Amixer as claimed in claim 1, in which the feed section of the rotorcomprises a screw conveyor and the discharge section comprises aninverted truncated cone, further comprising a feed hopper secured to thefeed end of said chamber, said rotor being arranged inside the mixingchamber in such a way that the feed section projects outwards from thechamber to penetrate into said feed hopper, and a discharge ring on thedischarge end of said chamber having its internal wall in the shape of atruncated cone with a taper different from that of the discharge sectionof the rotor.
 3. A mixer as claimed in claim 2, further comprising meansto adjust the discharge area formed between the discharge ring of themixing chamber and the discharge section of the rotor by relative axialmovement of the parts forming said area.
 4. A mixer as claimed in claim3, in which the mixing chamber further comprises interspaces forcirculation therein of a heat exchange fluid, means to circulate saidfluid inside the rotor and inside the discharge section of the chamber.5. A mixer as claimed in claim 1, further comprising means forrelatively moving the rotor and mixing chamber along a common axis andin which the material feed and discharge are simultaneous andcontinuous.
 6. A mixer as claimed in claim 1, further comprisingclosable holes in said chamber which permit the introduction into thechamber of members for sensing the parameters of the operational processand/or of process material.
 7. A mixer as claimed in claim 1, in whichthe mixing chamber and the rotor are cylindrical.
 8. A mixer as claimedin claim 1, in which the mixing chamber and the rotor are slightlyconical.
 9. A mixer as claimed in claim 1, in which the feed section ofthe rotor comprises a screw conveyor while the discharge sectioncomprises an inverted truncated cone and the mixing section has atriangle as the cross-section of its screw and prismatic parts.
 10. Amixer as claimed in claim 9, in which the corners of the triangle ofsaid section are bevelled according to a circumference concentric withthe axis of the mixing chamber and rotor.